Oxygen concentrators are commonly used in the home medical market to treat patients with chronic obstructive pulmonary diseases. Due to the wide availability of these oxygen concentrators on the market, the market for these devices is highly cost competitive and is expected to become even more competitive in the future. In order to remain competitive in this market, it is critical to reduce the manufacturing cost associated with every component in the oxygen concentrator system. The flow measurement and control system is one aspect of the overall concentrator system that may be cost-reduced; however, a less expensive flow system will only be viable if it provides sufficient accuracy and reliability.
Commercially available oxygen concentrators generally use one of two technologies to control the flow of product gas. The most common is a rotameter (flowmeter with a floating ball) combined with a manually controlled needle valve. Rotameters may be inexpensive, but in order to maintain accuracy, they are often coupled with a pressure regulator. Even combined with the regulator, due to pressure variations downstream of the rotameter, these needle valve/rotameter combinations provide an accuracy of about 10% which is sufficient for most home medical oxygen concentrators. Nonetheless, once combined with a regulator, this control method would not be considered inexpensive.
Another common technology is the use of an orifice plate in combination with a pressure regulator. The orifice plate usually contains 10 or more precision orifices, each providing an exact flow when an exact pressure is provided on the feed side. The regulator is used to provide a fixed pressure on the feed side. The orifice plate/regulator combination functions by allowing the user to adjust a dial to a specific orifice in order to provide a specific product flow. This method of flow control is generally more accurate than a rotameter; however, it is also more expensive and is also subject to inaccuracy due to downstream pressure fluctuations.
A need clearly exists for a low-cost, accurate flow control system for an oxygen concentrator. One method of achieving this goal makes use of the increasingly common use of acoustic systems to measure oxygen concentration in oxygen concentrators. For negligible additional cost, these acoustic systems can be modified to measure oxygen flow in addition to concentration. Coupling the flow measurement with an inexpensive motorized valve would result in a low-cost, accurate flow control system.